AGM batteries are able to withstand deep discharges with less damage than their conventional counterparts. Absorbed glass matt batteries are about 30% larger and heavy per nominal amp/hour. Their ability to be charged thoroughly and discharged more deeply make them an ideal choice for wind energy storage.
AGM batteries have their electrolyte (water/acid mix) trapped within a glass fibre matrix. Whilst charging, oxygen produced on the positive plate, aided by pressure formed within the batteries' airtight cells, recombines with hydrogen from the negative plate, forming water otherwise lost through the charging process. This recombining process enables the batteries to continue to be charged at a high rate without any water loss. These batteries are thus maintenance free.
Charging a 35Ah battery with a Rutland 504 wind turbine in high winds from flat will take approximately 5 hours.